An air intake filter removes particulate matter from air entering an air intake manifold of a motor vehicle. A variety of filter shapes have evolved over time for this purpose, such as flat panel, ring, cylindrical and frustoconical (section of a cone) designs. While air filters have largely served the purpose of removing particulate matter, such as dirt or debris, from the air entering the air intake manifold, such filters provide little help in preventing evaporative emissions from leaking out of the intake manifold and entering the atmosphere. Such emissions, arising chiefly when the engine is turned off and the intake manifold is hot, are a well-known contributor to air pollution.
During operation of an internal combustion engine, an airflow is drawn through the air intake system into an intake manifold and then finally into combustion chambers of the engine. The airflow is caused by the intake stroke of pistons within the engine, which forms an internal pressure within the intake manifold that is lower than the atmospheric pressure of the environment, and thus outside air is drawn into the air intake system. Evaporative emissions are prevented from exiting the air intake system due to the low internal pressure within the intake manifold and the airflow into the air intake system during operation of the internal combustion engine.
After engine shut-down, air continues to rush through the air intake system until the internal pressure within the intake manifold equals the atmospheric pressure of the environment. Evaporative hydrocarbons may be emitted if un-combusted fuel is present in the air intake system, such as due to pressurized fuel leaking from fuel rail(s) into the intake manifold through fuel injectors. This small amount of fuel may vaporize, and the resulting hydrocarbon vapor may migrate out of the air intake system into the atmosphere. Although such hydrocarbon vapor egress was once considered negligible, current regulations and environmental awareness have created a desire to eliminate evaporative emissions from the air intake systems of internal combustion engines.
Attempts to eliminate evaporative hydrocarbon emissions have included placing secondary, hydrocarbon adsorbing filters directly across the path of airflow into the air intake system. As will be appreciated, however, disposing extra layers of filtration media across the airflow path causes an additional flow restriction to be placed onto the air intake system. As such, the internal combustion engine is generally less efficient, or the air intake system may need to be increased in size so as to compensate for the increased flow restriction.
Other attempts to eliminate evaporative hydrocarbon emissions have included combining hydrocarbon vapor-adsorbing materials with conventional air filters. One drawback associated with these combination filters includes vapor-adsorbing materials flaking out of the combination filter and entering the air intake system. Further, such a loss of vapor-adsorbing materials may adversely affect the vapor absorbance of the combination filter. Accordingly, there is a need for eliminating hydrocarbon leakage from air intake systems of internal combustion engines without adversely affecting engine performance.